Signal processing

Abstract

The disclosed electronic apparatus comprises: transmitting means 54 arranged to transmit an ultrasonic signal; receiving means 55 arranged to receive a reflection of the ultrasonic signal from an input object, and to generate a received analogue electrical signal therefrom; a filter 56 arranged to take the received analogue electrical signal as input and to output a filtered analogue electrical signal; and digital processing means 52 configured to control a characteristic of the filter 56, and to use the filtered analogue electrical signal to determine a user input to the electronic apparatus.

1 . Electronic apparatus comprising:
 a transmitter arranged to transmit an ultrasonic signal;   a receiver arranged to receive a reflection of the ultrasonic signal from an input object, and to generate a received analogue electrical signal therefrom;   a filter arranged to take the received analogue electrical signal as input and to output a filtered analogue electrical signal; and   a digital processor configured to control a characteristic of the filter, and to use the filtered analogue electrical signal to determine a user input to the electronic apparatus.   
     
     
         2 . Apparatus as claimed in  claim 1  comprising a portable device. 
     
     
         3 . Apparatus as claimed in  claim 1  wherein the filter comprises one or more digital components. 
     
     
         4 . Apparatus as claimed in  claim 1  wherein the processor is arranged to determine how to control the filter based on an analysis of signals the processing means is currently receiving, or has previously received. 
     
     
         5 . Apparatus as claimed in  claim 1  wherein the characteristic of the filter controlled by the processor is whether the filter is enabled or not. 
     
     
         6 . Apparatus as claimed in  claim 1  wherein the filter has two or more modes of operation, with the processor able to select one or more of these modes. 
     
     
         7 . Apparatus as claimed in  claim 6  wherein the filter selectively either passes audible sound while removing ultrasound, or passes ultrasound while removing audible sound and arranged such that the processor can switch the filter between these two modes depending on whether the device is attempting to receive audible input or ultrasonic input. 
     
     
         8 . Apparatus as claimed in  claim 1  wherein the characteristic of the filter controlled by the processor comprises which frequency band or bands are to be filtered or passed. 
     
     
         9 . Apparatus as claimed in  claim 8  wherein the bands together span a continuous frequency range. 
     
     
         10 . Apparatus as claimed in  claim 8  comprising a multi-band filter controlled by the processor so as to remove signals outside a band encompassing the reflected signals from the input object, when receiving a user input. 
     
     
         11 . Apparatus as claimed in  claim 1  wherein the filter comprises a variable bandpass filter, with the digital processing means being configured to control the variable filter so as to output a succession of analogue electrical signals that have been filtered using different respective bandpass ranges. 
     
     
         12 . Apparatus as claimed in  claim 1  wherein the filter comprises a plurality of bandpass filters collectively arranged to output a plurality of analogue electrical signals simultaneously. 
     
     
         13 . Apparatus as claimed in  claim 1  wherein the filter is arranged to provide phase information relating to the filtered analogue electrical signal. 
     
     
         14 . Apparatus as claimed in  claim 13  wherein the filter comprises a sine filter and a cosine filter for each of a plurality of frequency ranges. 
     
     
         15 . Apparatus as claimed in  claim 1  wherein the filter comprises a plurality of sub-filters which are selectively couplable to an AD converter. 
     
     
         16 . Apparatus as claimed in  claim 1  wherein the filter comprises a plurality of sub-filters and comprising a plurality of AD converters, with each sub-filter being coupled to a corresponding AD converter. 
     
     
         17 . Apparatus as claimed in  claim 1  wherein the transmit signal comprises a chirp. 
     
     
         18 . Apparatus as claimed in  claim 1  wherein the processor is configured to cause the device to transmit different chirps depending on circumstances, and further wherein the processor is configured to control the filter so as to apply a de-chirp operation for a previously-transmitted chirp signal. 
     
     
         19 . Electronic apparatus comprising:
 a transmitter arranged to transmit an encoded ultrasonic signal;   a receiver arranged to receive a reflection of the ultrasonic signal from an input object, and to generate a received analogue electrical signal therefrom;   a filter arranged to take the received analogue electrical signal as input and to output a filtered analogue electrical signal, wherein said filter is adapted so as at least partially to apply pulse-compression to said analog electrical signal; and   a digital processor configured to use the filtered analogue electrical signal to determine a user input to the electronic apparatus.   
     
     
         20 . Apparatus as claimed in  claim 19  wherein the filter is arranged to remove from the received signal a contribution arising from energy in the transmit signal that has travelled along a direct path from the transmitter to the receiver. 
     
     
         21 . Apparatus as claimed in  claim 20  wherein the digital processor is configured to provide to the filter an estimate of the contribution to the received signal arising from signals which travel along the direct path and wherein the filter is arranged to use said estimate when filtering the received signal. 
     
     
         22 . Apparatus as claimed in  claim 21  arranged to sign-reverse said estimate, pass said estimate through an DA converter, and superimposes the reversed, analogue estimate on the received analogue signal. 
     
     
         23 . Apparatus as claimed in  claim 20  comprising a feedback arrangement configured to refine the estimate of the direct-path contribution and/or to synchronise the superimposing operation so as to provide effective subtraction. 
     
     
         24 . Electronic apparatus comprising:
 a transmitter arranged to transmit an ultrasonic signal;   a receiver which receives i) a direct path signal from the transmitting means; and ii) a reflection of the ultrasonic signal from an input object, and to generate a received analogue electrical signal therefrom;   a filter arranged to take the received analogue electrical signal as input and to output a filtered analogue electrical signal, wherein said filter is adapted to reduce a contribution of the direct path signal in the analogue electrical signal relative to a contribution of the reflected signal; and   a digital processor configured to use the filtered analogue electrical signal to determine a user input to the electronic apparatus.   
     
     
         25 . Apparatus as claimed in  claim 24  wherein the transmitter comprises one or more transmitters capable of generating ultrasound and the receiver comprises one or more receivers capable of receiving ultrasound. 
     
     
         26 . A method of determining a user input to an electronic apparatus comprising:
 transmitting an ultrasonic signal;   receiving a reflection of the ultrasonic signal from an input object;   generating a received analogue electrical signal from the reflection;   filtering the received analogue electrical signal in a filter which outputs a filtered analogue electrical signal; and   controlling a characteristic of the filter with a digital processing means; and   using the digital processing means to determine a user input to the electronic apparatus from the filtered analogue electrical signal.